In industrial applications, industrial hygienists are required to take periodic samples of the atmospheric breathing air in a given location. Hand-held, hand-operated air sampling pumps can be used to take such an air sample by drawing air through a chemical-reactive, colorimetric detection tube to determine the concentration of a certain chemical in the air sample.
There are several different types of manually-actuated hand-held sampling pumps that have been used to draw samples through detector tubes. These types may be, for example, a rubber or plastic squeeze bulb, a compressible bellows with spring return, or a manual or spring return piston pump.
The basic concept behind each of these pumps is to draw a specific volume of air sample through a colorimetric detection tube. The detector tubes are calibrated to react, by producing a stain length along a reactive agent inside of the tube as a specific volume of air, for example, 100 mL is drawn through the tube. The tubes can be calibrated to work with various volumetric sizes of samples. Once the volumetric flow is determined, however, it is essential that the precise amount of air be drawn through the tube during sampling. Accordingly, the accuracy of the concentration readings of the tube is directly proportional to the accuracy of the sample volume. For this reason, it is important that a sampling pump consistently draw an accurate amount of sampled air through the detector tube.
The three types of pumps are all similar in one aspect. In order to draw a sample of air, an air chamber inside of the pump is compressed or evacuated during a compression step. The evacuation of the air chamber causes a vacuum to form inside of the chamber. The vacuum then begins to dissipate by drawing air back into the air chamber through the detector tube.
Each type of pump provides a certain amount of accuracy and ease of operation. Ease of operation is an important feature of any sampling pump in that in many sampling situations, the pump must be able to be operated with one hand, for example, when a sample must be taken while climbing a ladder on a railroad car or a storage tank.
Of the three types of sampling pumps known, none can provide both accuracy, in drawing consistent volumes of air, and one-handed operation. The squeeze bulb type pump can be operated with one hand, however, it cannot draw consistent volumes of samples due to the inefficiency of evacuating its air chamber. An example of such a pump is the Thumbpump.TM. manufactured by Mine Safety Appliances Company, Pittsburgh, Pa. The piston pump is accurate in drawing sample amounts, however, the pump requires two hands to draw a sample. An example of a piston pump is the sampling pump manufactured by Sensidyne of Largo, Fla. The third pump, a spring-return bellows pump can provide both accuracy and one-hand operation. However, bellows pumps such as the Model 800-26065 manufactured by Dragerwerk AG Lubeck of the Federal Republic of Germany, cannot provide accurate results as the bellows cannot be completely and consistently evacuated during every compression step. The bellows of the Drager pump is comprised of two return springs and a rubber sleeve. Since the return springs of the bellows act alone as the stabilization frame of the pump, the bellows has a tendency to "cock" or deform during the compression step dependent upon how the user applies a force to compress the bellows. This results in a non-complete evacuation of the air chamber and an incomplete volumetric sample. Non-complete sampling can result in errors of 10-15% in determining the concentration of a chemical in the sample.
In all of these designs, a vacuum can still exist inside of the air chamber even though a visual inspection indicates that a complete sample has been drawn. In the piston type pumps, pressure indicators have been added to show when the vacuum has dissipated inside of the air chamber to indicate that a complete sample has been drawn. This feature is shown in the Sensidyne pump.
It would thus be desirable for a pump to provide the features of simple one-hand operation while drawing consistently accurate samples. It is the object of this invention to provide a hand-held air sampling pump that can be operated by one hand while consistently extracting precise volumes of sampled air from the atmosphere.